1. Field of the Invention
This invention relates generally to speed sensor devices and more particularly to a speed sensor device incorporating a reed switch which is controlled by the changes in the density of the magnetic flux occurring in response to the displacement of a permanent magnet.
2. Description of the Prior Art
In a conventional speed sensor device of this type, where a reed switch enclosed in a glass pipe is used, it is feared that the glass pipe will be damaged and that the electric contact between the reed switch and the lead wire will become defective. Further there is a disadvantage that the sensor device cannot be installed in a portion which is subject to strong vibration.